1. Field of the Invention
The present invention relates to pressure containers that are filled with various compressed gases such as CNG (compressed natural gas), various liquefied gases such as LNG (liquefied natural gas), LPG (liquefied petroleum gas), high-pressure hydrogen gases and other various pressurized substances.
2. Related Art
For pressure containers that are filled with various pressurized substances such as various compressed gases and various liquefied gases, generally employed are those that comprise a hollow resinous liner and a metallic opening metal fitted thereto. For ensuring the pressure resistance of pressure containers, in general, the outer peripheries of the liner and the opening metal are coated with a reinforcing member that satisfies predetermined pressure resistance standards.
In this case, in general, the metallic opening metal is worked to have a flange that extends toward the periphery of the container body at the bonding part thereof at which it bonds to the container body, and a part of the liner that abuts the flange is worked to have a self-sealing part that abuts the flange to be sealed up together, for ensuring the air tightness inside the pressure containers. Recently, some developments have been made for further ensuring the bonding of the self-sealing part to the flange in such pressure containers (e.g., U.S. Pat. No. 5,979,692).
FIG. 1 is a partly-enlarged, schematic cross-sectional view that shows the liner and the opening metal of the conventional pressure container illustrated in U.S. Pat. No. 5,979,692. The container 101 is so constructed that its flange 102 has a groove 103 that extends toward the direction of the wall thickness and a part of the self-sealing part 105 gets into the groove 103. Thus constructed, the self-sealing part 105 well bonds to the flange 102, and the opening metal 106 and the liner 107 are therefore well sealed up together at their bonding part to ensure the air tightness in the inside area 108 of the pressure container. In addition, the anchor part 110 that gets into the groove 103 of the self-sealing part 105 serves as an anchor of the self-sealing part 105. Therefore, when the container body 111 is filled with a pressurized substance and even when it is thereby expanded, the bonding between the self-sealing part 105 and the flange 102 is still kept as such owing to the anchor effect of the anchor part 110, and the seal ability of the self-sealing part 105 is therefore ensured.
Even in such pressure containers, however, the stress concentration in the resinous liner is great and the liner may be thereby broken or damaged. Anyhow, the seal ability of the pressure containers is not always satisfactory, and it is desired to develop pressure containers of improved seal ability and increased reliability.
Further, as for materials, Iron materials or steels have heretofore been used for the gas containers filling various gases therein. However, since iron has a large specific gravity, 7.9, gas containers formed of iron are problematic in that their weight is large. For example, when such gas containers are filled with fuel gas and mounted on vehicles, it is problematic in that the fuel expenses for vehicles increase. Not limited to such cases, in addition, when the container weight increases, then it causes various problems in that the containers are difficult to handle and the container shapes are limited since the mold ability of iron material is not good. Therefore, gas containers formed of other materials such as aluminium or resin are developed these days.
Of those, resin is expected to be a material capable of realizing gas containers that are lightweight and are given a lot of latitude in their shape, since its impact resistance is good, it is lightweight and its mold ability is good. When a resin material is used in forming gas containers, it must have a gas-barrier property of shielding gas penetration through it. When such a resin material is selected and used in forming gas containers, then the gas containers formed generally have a multi-layered structure that comprises a gas-barrier layer as the inner layer of the hollow gas container body and an FRP layer as the outer layer for ensuring the pressure resistance of the body. This is for preventing the resin material to form the gas containers from being fatigued owing to repeated expansion and contraction of the containers that are subjected to repeated filling and discharging of compressed gas in and out of them (e.g., Japanese Patent Publications Nos. JP-A 8-1813, JP-A 8-219392).
The gas containers described in JP-A 8-1813, JP-A 8-219392 comprise a gas-barrier layer formed of a resin material such as polyethylene resin, polypropylene resin, polyamide resin, ABS resin, polybutylene terephthalate resin, polyacetal resin or polycarbonate resin, and an FRP layer formed by winding up melt resin-infiltrated carbon fibers or glass fibers around it as the outer layer thereof. The resin materials mentioned above have a good gas-barrier property against gases having a large molecular weight, and therefore can be used, for example, for gas containers to be filled with CNG (compressed natural gas).
The above-mentioned various resin materials have a good gas-barrier property against gases having a large molecular weight, but could not exhibit their gas-barrier property against gases having a small molecular weight such as hydrogen gas. Accordingly, in order that the containers can be filled with gases having a small molecular weight, an additional gas-barrier layer of a resin material except the above-mentioned ones must be formed.
On the other hand, ethylene-vinyl alcohol copolymer resin (EVOH) is used as a resin material to form a gas-barrier layer (e.g., Japanese Patent Publication No. JP-A 11-123768). Since EVOH exhibits a good gas-barrier property even against gases having a small molecular weight, it is favorable for the gas-barrier layer against hydrogen gas, etc. On the other hand, however, its low-temperature impact resistance is poor, and the resin is therefore problematic in that it could not have satisfactory mechanical strength at low temperatures, for example, at −30° C. or lower.
In addition, the conventional gas containers as in JP-A 8-1813, JP-A 8-219392 and JP-A 11-123768 are resistant to pressure of 35 MPa or so. However, depending on their service condition, it is often desired that the pressure resistance of gas containers is further increased and gases of higher pressure are filled into them. Specifically, if gases of higher pressure could be filled in containers, then the frequency of exchanging gas containers and the frequency of gas charging into containers could be reduced. This saves users' labor and enables long-term use of gas-charged containers. However, the pressure resistance of the gas containers formed of conventional resin materials is unsatisfactory when they are filled with high-pressure gases. Given that situation, it is desired to develop resinous gas containers that have further increased pressure resistance.